The primary objective of the proposed work is to develop hydrophilic polymeric microspheres (beads) suitable to label membrane receptors and to separate cell subpopulations by means of immunological techniques. A new class of microspheres based on 4-vinyl pyridine was investigated and applied to labeling of Fc receptors. Polyglutaraldehyde in the form of heads of about 0.1 to 10 microns in diameter was found to bind immunoglobulins and other proteins. A study of magnetic immunomicrospheres for cell separation is in progress.